Invasive tumor cells presumably express certain genes which are inactive in non-invasive cells. We are attempting to clone these genes by making cDNA from an invasive cell line and extensively hybridizing it against RNA from a non-invasive cell line. We then label the remaining single-stranded DNA to use as a probe of a cDNA library from an invasive cell line. This approach should identify those clones which are expressed in invasive cell but not benign cells.